1. Field of the Invention
This invention relates generally to a contrast control circuit and, more particularly, to a contrast control circuit for adjusting the contrast of an analog electronic image information signal without changing its brightness range.
2. Description of the Prior Art
Electronic image printing devices for electronically printing an image on a photosensitive material such as a photographic film are well known in the art. Such devices may utilize a cathode ray tube (CRT) which responds to an analog electronic image information signal to expose a photosensitive material and thereby record the desired image. Alternatively, photosensitive materials may be exposed by laser beams scanned across the face thereof or light emitting diode arrays both of which are well known in the art. In addition, other means for converting an analog electronic image information signal to a hard copy by exposing a photosensitive material to either light or thermal energy are well known in the art.
Such photosensitive materials and in particular photographic films have determinate ranges of sensitivity to which the exposing light or thermal energy must be matched thereby requiring the exposure to take place within a select range of brightness values. However, it may also be desirable to vary the contrast of the image recorded on the photosensitive material which generally cannot be achieved without having some effect on the brightness range to which the photosensitive materials are exposed.
Therefore, it is a primary object of this invention to provide a contrast control circuit for use in an electronic image copying system for adjusting the contrast of an analog electronic image information signal without changing the brightness range thereof.
It is a further object of this invention to provide a contrast control circuit for use in an electronic image printing system for adjusting the contrast of an analog electronic image information signal without changing the selected maximum and minimum brightness levels thereof thereby maintaining the exposure of a photosensitive material such as photographic film within its selected range of sensitivity.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a circuit possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.